A high speed scanning heterodyne interferometer for in process surface measurement

A high speed scanning heterodyne optical interferometer for surface measurement is introduced. The interferometer employs a pair of Acousto-Optical Deflectors (AOD) which provides a fixed frequency difference between the reference and measurement arms to implement rapid scanning for surface measurement. There is no mechanical moving part involved in the scanning; therefore the phase noise created by mechanical scanning which restricts its speed has been reduced. The measurement arm and the reference arm are identical which reduces the sensitivity of the interferometer to change of ambient temperature. The experiment has demonstrated the potential of on-line measurement of surface finish in the nanometre range.